Re: detecting rename->commit->modify->commit

[Jeff King <peff@peff.net>]

On Thu, May 01, 2008 at 05:10:24PM +0300, Ittay Dror wrote:

> Say I have a file A, I rename to 'B', commit, then change file B and  
> commit. Does 'git diff -M HEAD^^..' detect that? From what I see now, it  
> will show 'B' as new (all of it with '+' prefix in the output). Am I 
> right?

Yes, it should find it, assuming the changes to B leave it recognizable.
Try:

  mkdir repo && cd repo && git init
  cp /usr/share/dict/words A
  git add . && git commit -m added
  mv A B && git add B && git commit -a -m rename
  echo change >>B && git commit -a -m change
  git diff -M HEAD^^.. | head -n 7

You should see something like:

  diff --git a/A b/B
  similarity index 99%
  rename from A
  rename to B
  index 8e50f11..6525618 100644
  --- a/A
  +++ b/B

However, note the similarity index. If you change B so much that it
doesn't look close to the original A, then the rename is not detected
(and intentionally so -- the argument is that it is no longer a rename
in that context, but a rewritten file).

-Peff